SOME QUESTIONS ANSWERED
DUNE-BUILDER A very specialised plant which gets the nickname of dune-builder is Marram grass (see Plant ID). Marram is a lonesome pioneer spreading out into loose, bare sand where it somehow finds nourishment while its roots bind the sand together. When we move inland to where the dunes are more vegetated and the whitish sand is darkened to a greyish-brown soil by decaying, organic matter, Marram is absent. Downhill J.A.
Q. HOW DO TIDES WORK? GRAVITY In a word, gravity! Tides are measurable, rhythmic and predictable twice-daily movements of our seas and oceans. It is principally the combined pulling powers of the sun and the moon on our seas that cause the tides. Our orbiting moon ‘pulls’ the water after it and as we all orbit the sun, we come under it’s immense gravitational pull too. Our own planet’s gravity and the friction of the sea bed, counters these influences to some degree. In addition, the rotation of the Earth, the great ocean currents of the world, the wind, the shape of the land above and beneath the sea and the texture of the sea bed all combine to influence the speed and direction of the tides. The difference in times between every high and low tide is roughly 12.5 hrs
which is half the time it takes the moon to circle the Earth hence we get two high and two low tides every 24 hrs. However rather than one great progressive tide circling the earth, there are a number of local tides differing greatly in the areas they cover. All coastal and near shore life including the activity of the human beach visitor is influenced by tidal movement. SPRINGS AND NEAPS Because our orbiting patterns vary seasonally we also see seasonal trends in our tides. More noticeably, as the sun and moon occur opposite to each other (with us in the middle) we experience extremely high tides (springs) and when at right angles to each other we experience the least tidal movements (neaps). (see later for safety information on tides).
Published on Jun 15, 2011